1. Field of the Invention
This invention relates to an improved level measuring device used to monitor the level of a substance in a container, for example to such a device which may be used to measure the level of fuel in the fuel tank or the level of brake fluid or coolant in motor vehicles.
2. Description of the Prior Art
For many years, level measuring devices for tanks have been known in which the buoyant body of a rotatably supported float assembly floats on the liquid in the tank. The angular position of the float, which depends on the level of the liquid, is transmitted for instance to a magnet, whose angular position is then a measure of the fill level. Such level measuring devices with float levers are known for instance from German Patent Disclosure DE-A 28 30 518 or German Patent Disclosure DE-A 199 25 185.
Other fill level sensors in the prior art are based on the use of feeler plates, changes in capacitance or resistance, thermal, radiometric, optical or acoustical measurements, radar measurements, force or pressure measurements, or measurements with a vibrating piezoelectric pickup.
One disadvantage of the sensors in the prior art is that between the sensor element and evaluating electronics there must usually be an electrical, mechanical or optical connection. This requires increased engineering effort and expense, for example, and the connection can become soiled by the substance, and/or the container can be made to leak because of the connection.
If an electrical, mechanical or optical connection is not required, then in the prior art at least the sensor element must be supplied from an energy source (such as a battery), which has to be changed after some time. This is especially disadvantageous in applications where access to the sensor element is difficult.